Daylight and Sunlight Assessments in Harrow

Harrow is a suburban borough of generous plots and detached houses, which makes it easy to assume daylight is rarely an issue. In practice the opposite is often true: the semis of Pinner, Hatch End and Rayners Lane sit with their flank walls a couple of metres apart, the large houses of Harrow on the Hill and Stanmore have neighbours whose gardens are the main concern, and the office buildings and bungalows of Kenton, Wealdstone and Harrow town centre are being replaced with flats that need a defined massing before anyone draws a façade.

Harrow is also one of the boroughs with its own geometric test, the 45 Degree Code in the Residential Design Guide SPD, and officers regularly ask for that check and the 25-degree test to be included alongside the BRE results. Our daylight and sunlight assessments in Harrow therefore usually cover both, and the three examples below show the range: an objection answered, a report expanded at the council's request, and a maximum envelope study for a developer.

Recent daylight and sunlight assessments in Harrow

Orley Farm Road, Harrow on the Hill: a neighbour's concern about sun to their garden

A part single, part two-storey rear extension, replacing a flat roof near the shared boundary with a pitched one. While the application was live, a neighbour raised concerns that the new roof would reduce light to their garden border, and the architect wanted an objective sun-path analysis. The neighbouring windows and garden all met the BRE guidelines, with the sun-on-ground result showing only a small part of the garden affected. Before-and-after shadow diagrams let the officer and the neighbour see the comparison. The report was submitted to the council to address the concerns raised.

Sequoia Park, Pinner: a report expanded when the officer asked for more

Side and rear extensions to a detached house in Pinner, tested against the windows and gardens of both adjoining neighbours; every one met the BRE guidelines. During the application the officer asked for fuller justification for the closest windows, including the 45-degree and 25-degree checks in Harrow's Residential Design Guide, and the architect lowered the design. The revised scheme again met the guidelines at every window and garden, and the amended report set out results for each window alongside the SPD geometric tests.

Mayfield Avenue, Kenton: a maximum envelope study for a developer

Redevelopment of a house and an adjoining office building off Mayfield Avenue as new duplex units. Rather than test a fixed design, the developer asked for the largest massing that would still meet the BRE guidelines for the adjoining house and its garden. The neighbour's windows kept well over 80 per cent of their daylight even with substantial extra height; the garden's sun on ground was the governing constraint. Reducing the rear and sloping back the front block kept the garden at the threshold. The report defines that envelope and is now the basis for the planning drawings.

What Harrow planning officers look for

Harrow now determines applications against the Harrow Local Plan 2021-2041, adopted in March 2026, which replaced the earlier Core Strategy and Development Management Policies, read with the London Plan. Its design and amenity policies require new development to safeguard the living conditions of neighbouring occupiers, including satisfactory daylight, sunlight and outlook, with particular attention to habitable rooms and kitchens.

Harrow's distinctive tool is the 45 Degree Code in its Residential Design Guide SPD, which tests the relationship between an extension and a neighbour's nearest window against a 45-degree line, with a 25-degree check for taller elements. Where a proposal breaches or is borderline against the code, officers expect the light impact to be examined fully through a BRE 209 assessment, and as the Sequoia Park job shows they may ask for the SPD checks to be written up in the same report. Our 45-degree rule blog explains how the code relates to the BRE tests. The technical benchmark is BRE 209: Site layout planning for daylight and sunlight (2022 edition). The Local Plan is at harrow.gov.uk/planning-developments/local-plan and the Residential Design Guide SPD at harrow.gov.uk/planning-developments/residential-design.

When you need an assessment in Harrow

• A rear or side extension to a semi in Pinner, Hatch End, Rayners Lane or North Harrow that breaches the 45 Degree Code from a neighbour's nearest window
• A pitched roof or two-storey element close to a boundary in Harrow on the Hill or Stanmore, where the neighbour's garden rather than their windows is the concern
• A neighbour's concern about light on a live application, where the officer needs figures and shadow diagrams rather than opinions
• Redevelopment of a house, bungalow or small office in Kenton, Wealdstone or Harrow town centre as flats, where a maximum envelope study fixes the massing before design work starts
• A Class MA conversion on Station Road, Harrow or Pinner High Street, where the new flats need adequate natural light
• Any application where a Harrow officer has asked for the 45-degree and 25-degree checks to be justified

How we work

Nick Maslen scopes the job, agrees a fixed fee up front and confirms which neighbours, gardens and tests the council will want. Milica or Ana builds the 3D model, reusing your SketchUp or Revit model where one exists, and runs the BRE 209 tests, usually within 4–5 working days of receiving the information we need. Shadow diagrams and the SPD geometric checks are added where they will help the officer. The four tests are:

• VSC (Vertical Sky Component): the sky still visible from each neighbouring window
• NSL (No-Sky Line): daylight distribution within each neighbouring room
• APSH (Annual Probable Sunlight Hours): annual and winter sunlight to windows within 90 degrees of south
• Sun on ground: the share of a garden receiving two hours of sun on 21 March

The tests are explained on our VSC, NSL and APSH page and the thresholds on our BRE guidelines page.

Frequently asked questions in Harrow

My extension breaches Harrow's 45 Degree Code. Is a BRE report worth doing?

Usually, yes. The code is a screening tool; a BRE 209 assessment measures the actual loss of daylight and sunlight at the neighbour's windows, and officers in Harrow accept it as the fuller justification the SPD anticipates.

A neighbour has raised evening sun to their garden. Can that be tested?

Yes. The sun-on-ground test measures the share of the garden receiving two hours of sun on 21 March, and we can add before-and-after shadow diagrams at specific times so the comparison is visible, as we did at Orley Farm Road.

Can you tell a developer how big a scheme can be before it is designed?

That is what a maximum envelope study does: we iterate the massing against the neighbours' windows and gardens until the envelope sits at the BRE thresholds, and hand over a defined volume to design within.

Get a fixed-fee quote

Send drawings and the address through our contact page or use the price calculator for an instant figure; Nick is on 01962 809155 and nick@sunlightassessments.co.uk. For sites south of the borough boundary, see our Brent page.